If I set up 2 PPP links on one Linux box, is there a way to force
packets to go through the Point-to-Point? That is, if they're on
separate boxes traceroute shows 2 hops, but if they're on the same box
it only shows one. I use

/sbin/route add -host dev ppp0

to set up the route when they're on separate hosts. So how to keep
Linux from short-circuiting the route and not using 2 hops? It looked
like maybe NAT would do it, but

/sbin/iptables -t nat -A OUTPUT -s --out-interface ppp0

results in a route to the p-t-p but not back.